PHOSPHATE EOCK : UTILIZATION AS FERTILIZER. 11 



Processes of this type, if practicable, would have an advantage over 

 the one now generally employed in that they produce available phos- 

 phoric acid from phosphate rock in a single operation, thus obviating 

 the necessity of first manufacturing sulphuric acid. Experiments in 

 the laboratories of the Bureau of Soils have shown, however, that 

 phosphate rock is very resistant to the action of sulphurous acid or 

 sulphur dioxide, and efforts to obtain complete decomposition of 

 phosphate rock by such treatments were unsuccessful. Further work 

 along these lines, however, seems desirable. 



The processes of Glaser 1 have for their object the production of con- 

 centrated phosphates by treating phosphate rock with sufficient dilute 

 sulphuric acid to produce phosphoric acid and then using this phos- 

 phoric acid as a solvent for more phosphate rock. 



They involve the well-known method of making double acid phos- 

 phate, a method admirably suited for the treatment of low-grade 

 phosphate rock containing but little iron and aluminum. The equa- 

 tions showing the reactions taking place in this process have already 

 been shown on page 10. The product usually requires artificial 

 drying, since it contains but little sulphate of lime. The patents of 

 Glaser have now expired. 



In order to produce a dry pulverulent product, Memminger 2 pro- 

 poses to mix calcium fluoride or fluorite with phosphate rock and then 

 treat the mixture with sulphuric acid. The generation of gaseous 

 compounds of fluorine, he claims, renders the acid phosphate porous 

 and thus facilitates the escape of moisture from the hot mass. 



While this procedure would no doubt produce a high-grade acid 

 phosphate, the poisonous nature of the fumes evolved during the 

 curing of the acid phosphate would make it objectionable to employ 

 such a method either in the vicinity of towns or in a farming country. 

 Moreover, it is questionable whether the extra quantity of acid 

 required to act upon the fluorite would not offset the advantages 

 gained. This patent expired in 1908. 



Hoyerman 3 devised a process to economize on the quantity of acid 

 required to produce available phosphoric acid. His process consists 

 in adding to phosphate rock a quantity of sulphuric acid sufficient 

 only to convert it into dicalcium phosphate, a product which has 

 practically the same trade value as monocalcium phosphate. 



Such a process, while theoretically possible, presents difficulties in 

 actual practice. The quantity of ordinary sulphuric acid required is 

 hardly sufficient to mix intimately with a large bulk of ground phos- 

 phate, and, therefore, the resulting mass is apt to contain a con- 

 siderable percentage of so-called unavailable phosphoric acid, owing 

 to the fact that some of the phosphate rock has not been acted upon. 



i United State* Patents Nos. 389666 (1888), 417820(1889), 459676 (1891). 

 ' United States Patent No. 146667 (1891). 

 » r, Patent No. 736730(1903). 



